The present invention relates to an improved ultrasonic welding machine for effecting metal-to-metal weldments, particularly weldments between dissimilar metals.
It is well known that ultrasonic welding between plastic materials requires the application of ultrasonic vibratory energy having a direction of vibration substantially normal to the plastic surfaces to be welded together. Similarly, it is also well known that ultrasonic welding between metal surfaces requires the application of ultrasonic energy having a direction of vibration substantially parallel to the metal surfaces being welded together. Additionally, it is essential that a static compression force be applied to urge the metal surfaces together during the welding operation.
Because of the fundamental difference in the direction of the vibratory energy with respect to the surfaces to be welded in the case of plastic welding as opposed to metal welding, prior art ultrasonic welding devices have been designed either for plastic welding or for metal welding, but not for both. Thus, a person wishing to perform both plastic and metal welding would have to use two separate welding machines, one designed for holding the workpieces with the surfaces to be welded oriented normal to the direction of vibratory energy and the other designed to hold the workpieces with the surfaces to be welded oriented substantially parallel to the direction of vibratory energy. Such a duplication of equipment could be prohibitively expensive.
Furthermore, prior art ultrasonic welding machines designed for metal welding typically apply the necessary static compressive force through the vibrational components, the static compressive force typically being exerted in a direction substantially normal to the vibratory force. Such prior art devices are disclosed, for example, in U.S. Pat. No. 3,017,792, issued to W. C. Elmore et al. on Jan. 23, 1962 and U.S. Pat No. 3,184,842, issued to N. Maropis on May 25, 1965. This application of the static compressive force and the vibratory forces in different directions through the vibratory members (horns, couplers, transducers, etc.) causes these vibratory members to sustain considerable bending forces, resulting in eventual fatigue of the vibratory members and, ultimately, failure thereof by virtue of the fatigue.
One prior art ultrasonic metal welder, disclosed in U.S. Pat. No. 2,946,119, issued to J. B. Jones et al. on July b 26, 1960 (see FIGS. 1 and 2), applies the static compressive force in a direction parallel to the vibratory force, but the static compressive force is applied through the vibration-transmitting member so that the vibrational path of that member is biased by the static compressive force. In other words, ideally if the vibration-transmitting member starts from an equilibrium position, it will vibrate equal distances below and above that equilibrium position during alternative half cycles of the vibration. But in the Jones et al. device the downward static compressive force applied through the vibration-transmitting member aids the vibrational movement in the downward direction and opposes the vibrational movement in the upward direction so that the excursions of the vibration-transmitting member below the equilibrium position are greater than the excursions above that position. This biasing of the vibrational movement can result in distortions in the resulting weld. Furthermore, the Jones et al. device is designed specifically for use in metal bonding and is not susceptible of use in plastic welding.